Improvements to thermodynamic solar heat transfer systems

ABSTRACT

The invention describes improvements to heat transfer systems applied to buildings, particularly those commonly referred to as Themodynamic or Solar Themodynamic.

The present invention is directed towards improvements to heat transfer systems, commonly referred to as thermodynamic or thermodynamic solar systems, designed to transfer heat from external environments to internal environments. More particularly, although not exclusively, the present invention is directed towards such systems in use in cooler climates and where the internal environments are buildings. More particularly the heat transferred is used to heat water, either to supply a radiative heating system or as a hot water supply to kitchens and bathrooms and so on. Such buildings may include domestic dwellings. Such a system is distinct from ‘air source’ heat exchange systems which typically utilise fans to blow air across evaporator and/or condenser parts of the system and run air conditioning/heating units within buildings.

A known prior art system, illustrated in FIG. 1, that is currently available comprises at least one aluminium panel (1) and a heat pump (2). A refrigerant fluid, R407c, (3) is entered to the panel as a liquid at −20° C. The panel is outside, and absorbs heat from ambient conditions (8), including the sun during daytime, which converts the liquid into a vapour. This vapour then passes into the heat pump (2), where it is compressed, raising the temperature of the vapour to approximately 80° C. This hot vapour (hot refrigerant vapour) is entered into a heat exchanger or condenser (10, 20), where the hot refrigerant vapour imparts its heat into water (5, 5 a, 5 b). The water temperature in the tanks (10, 20) is raised to approximately 55° C. The heated water (5 a, 5 b) is then used within a building (7) as a supply (5 a) to heating elements such as radiators, underfloor heating systems, or swimming pool heaters, and/or as a hot water supply (5 b) to kitchens, bathrooms and the like. In the illustrated example FIG. 1, tank condenser 10 represents a central heating storage tank and tank condenser 20 represents a domestic hot water supply providing hot water (5 b) to taps in the kitchen and bathroom of a house (7). The hot refrigerant vapour is directed as necessary to either the central heating tank (10) or the hot water tank (20) by means of a valve (30). The cooled refrigerant then passes into an expansion valve (6) before the cycle repeats. This system is in common usage in some southern European countries and has also been used in some northern European countries.

Where such a system is used in cooler climates, such as those found in some northern European countries, a problem of frosting or icing is not uncommon during cooler times of year. When the ambient outside temperature is low, and there is significant water vapour in the atmosphere, the fact that the liquid entering the panels is very cold (−20° C.) results in atmospheric water vapour freezing on the surface of the panels (1) as frost or ice. This results in a problem of loss of efficiency as heat transfer into the panel is impeded by the ice on the surface. This is exacerbated where the ambient outside conditions include precipitation of one form or another, such as snow or rain. There is a further issue of a potential safety risk as such ice can build up into a significant layer during the course of, for example, a winter. When the formed ice eventually thaws, it can slip from the panel. As such panels are often mounted on roofs or otherwise raised from the ground, this is a potential hazard to people or animals that might be standing beneath them or risk of damage to other objects beneath them.

What is needed is a suitable method of preventing such ice build-up on the panels of such systems where they are installed in an environment where this would be a potential problem.

Accordingly there is provided a heat transfer system suitable for generating hot water in at least one area of a building (7) comprising:

At least one heat transfer panel (1, 1 a) for taking in heat from an environment (8) to convert a refrigerant fluid (3) from liquid into vapour;

A heat pump (2) for compressing refrigerant vapour from the panel into hot refrigerant vapour, and;

A condenser (10, 20, 100) for transferring heat from the hot refrigerant vapour to water (5); Wherein the system further comprises means (60) for diverting the hot refrigerant vapour into the panel.

The diversion of hot refrigerant vapour into the panel, or hot gas defrost cycle, means that any frost that has built up on the panel due to environmental conditions can be melted away, or any ice that has built up on the panel can be loosened for controlled removal. It has been found that, in wintry conditions such as give rise to the problems previously noted, a 2-3 minute reversal of hot gas every few hours is sufficient to keep panels suitably frost-free.

A problem that newly arises as a result of this improvement is that of minimising the impact of this hot gas defrost cycle on the efficiency of the overall system. Any hot gas defrost cycle must be short in time interval and infrequent. Accordingly, in a further aspect of the invention, the heat transfer system further comprises a temperature sensor (70). This temperature sensor measures the ambient temperature conditions to which the panel is subject. The hot gas defrost cycle will only then initiate when the ambient conditions are cold enough to require it.

In a further aspect of the invention, the system comprises a humidity sensor (80). The humidity sensor measures the ambient humidity to which the panel is subject. The hot gas defrost cycle then only initiates when the ambient conditions to which the panel is subject include sufficient air moisture for frost or ice to form. This humidity sensor may operate in combination with the temperature sensor previously noted.

Preferably, the hot gas defrost cycle will only initiate when the combination of temperature and humidity are such that there is a likelihood of frost or ice forming on the panel or panels. Such a system could be automated and may comprise a computing or other control device (90) such as an Electronic Control Unit (ECU) which monitors the readings of the temperature sensor and/or humidity sensor, and regulates the time and frequency of use of the hot gas defrost cycle in response to these outputs so as to maximise the efficiency of the system, whilst still maintaining the desirable effects of the hot gas defrost cycle.

Existing system panels tend to be constructed of blown cold roll-bonded aluminium. Two flat sheets of aluminium are pressed together by mechanical rollers. A pattern of adhesive is laid on one of the flat sheets prior to the two sheets being laid together. The two sheets adhere together in accordance with the pattern—high pressure air is then forced between the sheets, and where the sheets are not bonded together, a channel is formed. Where the adhesive is laid appropriately, the channels will form a track or tracks through which, as in the prior art and present example, refrigerant can flow.

The walls (13) of the refrigerant channels of the prior art panels (1) have a typical thickness (14) of 0.7 mm. In systems according to the current invention, the wall thickness has to be more typically in the region of 0.9 mm. This is because the hot refrigerant vapour is at a greater pressure than the refrigerant fluid liquid or vapour passing through the panel when the system is running ‘normally’. The increased wall thickness is necessary to contain the increased pressure.

In a preferred embodiment, the refrigerant is an alternative refrigerant R-134a. This has various advantages described later herein, but also requires a panel capable of handling a higher pressure than in a system running on R407c. By way of example, a prior art system runs with a nominal pressure of up to approximately 12 bar maximum in a panel (1). A system according to the current invention, utilising R134a and also capable of running the hot gas defrost cycle, requires panels (1 a) capable of handling up to 25 bar.

The use of alternative refrigerant R-134a enables the system to produce hot refrigerant vapour at a higher temperature than would be obtainable with R407c. Typically, the hot refrigerant vapour can be at a temperature of up to (90° C.) as opposed to the approximately 80° C. of R407c as used in the prior art system.

This has the further advantage that the water supplied at the condenser (10, 20, 100) within the building area can be heated to a higher temperature than that of the prior art system, ie: 65° C. as opposed to 55° C., due to the higher temperature of the hot refrigerant gas.

The existing prior art system, where it is intended to produce a hot water supply as well as hot water for heating, requires two water tank/condenser units; one for heating the hot water (20), and one for heating the water for the heating system (10). This is illustrated in FIG. 1, where tank 10 is a central heating ‘buffer’ tank, and tank 20 is a hot water tank. The hot refrigerant gas in the system is typically available to one or the other of these tanks (10,20), depending on momentary requirement, and is directed towards one or the other tank by means of a valve (30).

Because of the fact that water for the hot water supply, in the prior art system, is stored in a tank (20), water in this tank will generally be subject to a temperature gradient. Furthermore, water in this tank may be subjected to several cycles of heating and cooling before being used and exiting the tank. Given the highest temperature point of the prior art system (55° C.), there is a potential issue with Legionella, as it is commonly reckoned that Legionella bacteria can survive at this temperature for anywhere between 1 to 6 hours.

Improvements enabled by the present invention provide a solution to this potential problem. In the system according to the current invention, there is only a single water tank/condenser unit (100). As noted above, hot refrigerant gas is piped through this tank (100) at 90° C., heating the contents to 65° C. The contents of the tank are part of a sealed system and circulate around to provide radiative heat in radiators, underfloor heating, swimming pool heating and the like. Water in the upper part of this tank (due to convection) may be generally maintained at the upper temperature range of the system, ie 65° C. Within this upper region of the single tank is a secondary heat exchange coil (40) through which cold mains water is piped on a demand basis. The cold water is heated as it passes through the coil and is then available as a hot water supply to taps and so on in areas such as kitchens and bathrooms. This system obviates the requirement for the storage of hot water in a hot water storage tank 20 and reduces the risk of Legionella.

This improvement also means that only one tank/condenser unit (100) is required instead of two (10,20) to provide both heating water and hot water where this is required. This saves space, makes system installation easier and is likely to reduce cost.

A further improvement to the prior art system is presented in the panels (1 a) in the system according to the current invention. These panels are specifically designed so that they may be mounted in any orientation, in contrast to prior art panels which will only work when they are fixed in a particular orientation. The current panels are also designed with a multiplicity of potential routes for refrigerant flow. Refrigerant entering the panel through an input/output port (11 a, 11 b) may split so as to follow any one of a number of routes around the panel before exiting the panel through the other input/output port (11 b, 11 a). However, the panel is specifically designed so that any potential route around the panel from 11 a to 11 b (or vice versa) is the same distance. An exemplary embodiment of this is shown in FIG. 4. The benefits of this design are that pressure distribution around the panel is more even than in a standard prior art panel, and the panel absorbs heat from its surroundings in a more efficient manner.

A further use of the system would be as a means of heat distribution in a desired manner in any particular building. In a building in a warmer environment, for example, there may be a requirement to cool certain rooms in a building and provide heat to others. For example, a hotel may wish to provide cooling in some rooms for the comfort of guests when the temperature is relatively high. The same hotel may maintain a swimming pool, which it wishes to keep at a temperature higher than even the ambient environmental temperature. Accordingly, a system in accordance with the currently noted improvements, or even a prior art system, may be installed with the panel (1, 1 a) in a room in which it is desired to lower the temperature. The system is otherwise as previously noted, with a condenser unit sited in another room and arranged so as to provide hot water to a swimming pool heating circuit. Similar arrangements may be made so as to provide central heating, underfloor heating, or even a hot water supply to other parts of the same building or even a building complex comprising a number of separate buildings. Cooling by means of the panel in one building, for example, may be provided, with the heat removed used to maintain a sauna in another building. The Hot Gas Defrost function in accordance with the current invention may be required in environments where ambient humidity is very high and frost or undesirable condensation may form on the panel or panels in the cooled areas of the building.

FIG. 2 shows an exemplary embodiment, not intended to be limiting, of a system in accordance with the current invention. Panel la sits outside of a house 7 in ambient external environmental conditions 8. Refrigerant moves around the system in the normal manner as shown by the arrows (3, 3 a). In this case, the refrigerant 3 is R-134a. Refrigerant enters the panel (la) as a liquid at −20° C. in the normal manner. The panel (1 a) has a more efficient channel pattern and is composed of a roll-bonded aluminium panel having channel walls 0.9 mm thick. Refrigerant vaporises in the panel la as it absorbs ambient heat and then passes through pipework (21) and into a 4-way valve (60), then through more pipework (22) into the heat pump (2), which compresses the R-134a and raises its temperature to 90° C. The hot refrigerant vapour then passes back through a further pipe (23), through the 4-way valve (60) and on through further pipework (24) into a hot water storage tank (100), which is a storage tank supply for a domestic heating system—cool water (5) heats up in the tank until it is hot water (5 a) at up to 65° C., which then moves out into an underfloor heating system or radiator heating system. Towards and within the top end of tank 100 is a coil (40) into which mains cold water (5 c) enters on an ‘on-demand’ basis, which heats up into hot water (5 b) as it passes through the hot upper region of the tank (100), which is then used to supply taps in the kitchen and bathroom of the dwelling (7).

A temperature sensor (70) and a hygrometer (80) monitor the temperature and humidity of the outside environment (8), and are monitored by an electronic control unit (ECU) (90). If the temperature and humidity are such that frost or ice formation on the panel is likely, the ECU activates the 4-way valve (60). This diverts hot refrigerant vapour from the heat pump (2) from pipe (23) back into the panel (1 a), and reverses the direction of flow as shown by arrows (3). This is the hot gas defrost cycle. The ECU runs the hot gas defrost cycle in accordance with a schedule determined by the severity of the cold and/or humidity so as to remove or thaw any such frost or ice, typically for 2-3 minutes every 3 hours. The ECU (90) is also able to run the hot gas defrost cycle on demand by a user, so that if the system had been inoperative for a period of time and the panel had become covered in lots of snow and/or ice, a 2-3 minute period of hot gas defrost cycle would loosen the covering and enable it to be brushed off easily by the user.

FIG. 3 illustrates an embodiment of a standard prior art panel (1), having an input (11 c) and an output (11 d) port and channels running through it (12).

FIG. 4 illustrates an embodiment of an improved panel (1 a) in accordance with the current invention. It has two input/output ports (11 a and 11 b). The channels (12) through which refrigerant or hot refrigerant gas can travel can be seen to follow a path such that any route through which refrigerant can pass from one port (11 a/11 b) to another (11 b/11 a) is of substantially equal length.

FIG. 5 shows a cross-section through a channel (12) along the line AA, illustrating that the walls (13) of the channel have a thickness (14). In prior art panels (1) this is typically up to 0.7 mm. In an exemplary embodiment of the current invention, the thickness of these walls is 0.9 mm.

FIG. 6 shows an embodiment of the improved system in accordance with the invention as previously described, wherein the environment (8) in which the panel (1/1 a) is situated is one room (8 a) within a building. In this instance, the panel (1/1 a) is providing cooling for this room, which is a larder (8 a). Tank 100 is providing hot water (5 a) for a heating circuit (52) for heating a swimming pool (54), and hot water (5 b) produced by the coil (40) is supplying a shower area (56).

Note that references to buildings, houses and/or dwellings are not intended to be limiting—it will readily be appreciated that various structures or collections of structures could have such systems installed and that the components of such systems may sit on or within a variety of locations, the reference drawings being non-limiting. Panels and sensors may sit on the outside of a building or on a pole or other structure next to a building. Various components of the system (heat pump, evaporator, for example), may be open to the elements or sit in wooden huts next to a building or may sit within a building. Buildings may include offices, hotels, restaurants or public buildings such as museums, town halls or sports centres, as well as houses or similar dwellings. 

1. A heat transfer system suitable for generating hot water in at least one area of a building comprising: at least one heat transfer panel for taking in heat from an environment to convert a refrigerant fluid from a liquid into a vapor; a heat pump for compressing refrigerant vapor from the panel into hot refrigerant vapor; and a condenser for transferring heat from the hot refrigerant vapor to a water supply; wherein the system further comprises means for diverting the hot refrigerant vapor into the panel.
 2. A heat transfer system as claimed in claim 1 further comprising a temperature sensor.
 3. A heat transfer system as claimed in claim 1 further comprising a humidity sensor.
 4. A heat transfer system as claimed in claim 1 further comprising a means for controlling the means of diversion of hot refrigerant vapor into the panel.
 5. A heat transfer system as claimed in claim 4 wherein the control means activates the diversion means in response to readings from the sensor or sensors.
 6. A heat transfer system as claimed in claim 4, wherein the control means is an electronic control unit or other computing device.
 7. A heat transfer system as claimed in claim 1 wherein the refrigerant fluid used is R-134a and reaches a temperature of up to approximately 90 degrees centigrade when in the hot refrigerant vapor phase.
 8. A heat transfer system as claimed in claim 1 wherein the panel is an aluminum roll-bonded panel comprising refrigerant channels with walls having a thickness.
 9. A heat transfer system as claimed in claim 8 wherein the wall thickness of the refrigerant panel is sufficient to withstand pressures of at least approximately 20 bar.
 10. A heat transfer system as claimed in claim 8 wherein the wall thickness of the refrigerant panel is sufficient to withstand pressures of at least approximately 25 bar.
 11. A heat transfer system as claimed in claim 8 wherein the wall thickness of the refrigerant panel is substantially greater than 0.7 mm.
 12. A heat transfer system as claimed in claim 8 wherein the wall thickness of the refrigerant panel is at least approximately 0.9 mm.
 13. A heat transfer system as claimed in claim 1 wherein the water supply is heated to a maximum of at least approximately 65 degrees centigrade.
 14. A heat transfer system as claimed in claim 13 further comprising a tank acting as a condenser for the hot refrigerant gas and in which a water supply is heated by the hot refrigerant gas and stored, wherein the tank further comprises a coil in which a second water supply is in turn heated by the stored hot water within the tank.
 15. A heat transfer system as claimed in claim 14 wherein the first water supply is used within a heating circuit in a building, and the second water supply is used as a hot water source.
 16. A heat transfer system as claimed in claim 1 wherein the panel is designed so that refrigerant fluid may take a number of different paths through the channels in the panel.
 17. A heat transfer system as claimed in claim 16 wherein the panel is further designed so that each different possible path is of substantially the same length.
 18. A heat transfer system as claimed in claim 1 wherein the environment is an external environment.
 19. A heat transfer system as claimed in claim 1 wherein the environment is a room or other area within a building.
 20. A heat transfer system suitable for generating hot water in at least one area of a building comprising: at least one heat transfer panel for taking in heat from an environment to convert a refrigerant fluid from liquid into a vapor; a heat pump for compressing refrigerant vapor from the panel into hot refrigerant vapor; and a condenser for transferring heat from the hot refrigerant vapor to a water supply; wherein the environment is a room or other area within a building.
 21. A heat transfer system as claimed in claim 1 wherein the means for diverting hot refrigerant vapor into the panel is a fluid control valve.
 22. A heat transfer system as claimed in claim 21 wherein the fluid control valve is a 4-way valve.
 23. A tank for use in a heat transfer system, which may act as a condenser for hot refrigerant gas and in which a water supply is heated by the hot refrigerant gas and stored comprising: a coil in which a second water supply is in turn heated by the stored hot water within the tank. 